(NBC News) — Three U.S. Army Special Forces soldiers were killed and two were wounded in Niger on Wednesday, in an ambush by suspected Islamic militants operating from Mali, multiple sources with knowledge of the incident told NBC News.

The Department of Defense announced Friday the soldiers were part of a joint U.S. and Nigerien train, advise and assist mission. All soldiers were assigned to 3rd Special Forces Group (Airborne), in Fort Bragg, North Carolina.

Killed were:

Staff Sgt. Dustin M. Wright, 29, of Lyons, Georgia

Staff Sgt. Bryan C. Black, 35, of Puyallup, Washington

Staff Sgt. Jeremiah W. Johnson, 39, of Springboro, Ohio

According to the sources, one soldier from Niger was also killed in the attack.

The U.S. military did not originally confirm the deaths officially, but did acknowledge that a “hostile fire” incident involving U.S. troops had occurred.

“We are working to confirm details of the incident and will have more information as soon as we can confirm facts on the ground,” said a spokesperson for Africa Command, or AFRICOM. The military generally does not confirm nor identify American casualties until it has ensured that the deceased’s family members have been properly notified.

White House Press Secretary Sarah Huckabee Sanders told reporters Wednesday night that Gen. John Kelly had briefed President Donald Trump on the incident.

The deaths throw a spotlight on one of the many military operations being conducted in Africa as part of a wide-ranging war on a variety of extremist groups, in a swathe of countries stretching across the continent. According to the French radio broadcaster RFI, a joint Nigerien-American patrol was ambushed near the village of Tongo Tongo, approximately 17 miles from the border with Mali.

“U.S. Forces are in Niger to provide training and security assistance to the Nigerien Armed Forces, including support for intelligence, surveillance and reconnaissance (ISR) efforts, in their efforts to target violent extremist organizations in the region,” said U.S. Navy Lt. Cdr. Anthony Falvo, in a statement released to NBC News. “One aspect of that is training, advising and assisting the Nigeriens in order to increase their ability to bring stability and security to their people.”